--- a/utils.h	2020-04-13 01:11:27.959275309 +0200
+++ b/utils.h	2020-04-13 01:11:38.213384799 +0200
@@ -3,6 +3,7 @@
 #include <stdio.h>
 #include <errno.h>
 #include <string.h>
+#include <sys/types.h>
 
 extern long buffering_write(int outf, char *buffer, long num);
 extern int buffering_close(int fd);
